High-strength brass alloy for sliding member, and sliding member

ABSTRACT

High-strength brass alloy having superior wear maintains single-structure β phase and Fe—Cr—Si-based intermetallic compounds dispersed in the β phase. A high-strength brass alloy for sliding member comprises Zn from 17% to 28%, Al from 3% to 10%, Fe from 1% to 4%, Cr from 0.1% to 4%, Si from 0.5% to 3%, mass ratio, and the remnant including Cu and inevitable impurities. The high-strength brass alloy has structure in which the matrix shows single-phase structure of β phase and Fe—Cr—Si-based intermetallic compounds are dispersed in the β phase. The high-strength brass alloy for sliding member has the structure in which the matrix shows single-structure of β phase and hard Fe—Cr—Si-based intermetallic compounds are dispersed in the β phase. Thus the hardness is increased and wear resistance is improved.

TECHNICAL FIELD

The present invention relates to high-strength brass alloy havingsuperior wear resistance, and particularly to the high-strength brassalloy suitable for use in a sliding member such as a sliding bearing ora sliding plate and to a sliding member using that high-strength brassalloy.

BACKGROUND ART

As conventional high-strength brass alloy used for a sliding member suchas a bearing, can be mentioned the high-strength brass casting classes1-4 prescribed in Japanese Industrial Standard JISH5120 (See Non-PatentDocument 1). These high-strength brass alloys are obtained by addingelements such as Al, Fe, Mn and the like to Cu—Zn alloy to improvecorrosion resistance in sea water, toughness, wear resistance andhardness, and used frequently for sliding applications such as asynchronizer ring in a transmission mechanism of an automobile, a gearwheel in an ordinary machine, and a bearing.

In the high-strength brass alloy, there appear various matrices such asα phase, β phase, α+β phase and γ phase according to zinc equivalents ofadded elements. When the zinc equivalent is smaller, α phase appears.Although the high-strength brass alloy in which α phase has appeared issuperior in toughness, its hardness is inferior and, when put to slidingapplications, easily shows abrasive wear. Further, when the zincequivalent is increased, β phase appears. Then with further increase ofthe zinc equivalent, γ phase appears. The high-strength brass alloy inwhich γ phase has appeared has the advantages of increased hardness andimproved wear resistance. But on the other hand, its toughness issignificantly reduced and its shock resistance becomes lowered.

Thus, in the sliding applications, the high-strength brass alloy whosematrix is single phase of β phase is widely used since its toughness isnot reduced and its wear resistance is superior. However, as efficiencyand longer life of mechanical equipment are promoted recently, it isdesired further to improve wear resistance of the sliding member of thehigh-strength brass alloy.

For improving wear resistance of the high-strength brass alloy havingthe matrix of α+β phase or β phase, is proposed the high-strength brassalloy having the matrix in which a manganese silicide type intermetalliccompounds such as Mn₅Si₃ are dispersed (See Patent Document 1, forexample), or the high-strength brass alloy having the matrix in whichFe—Mn—Si-based intermetallic compounds are dispersed (See PatentDocuments 2 and 3, for example).

DESCRIPTION OF THE RELATED ART Non-Patent Document

-   Non-Patent Document 1: Japanese Industrial Standard JISH5120

Patent Documents

-   Patent Document 1: Japanese Published Examined Application No.    51-41569;-   Patent Document 2: Japanese Published Examined Application No.    62-57700; and-   Patent Document 3: Japanese Published Examined Application No.    2-38651

SUMMARY OF INVENTION Technical Problem

Although it is known that dispersion of manganese silicide orFe—Mn—Si-based intermetallic compound in the matrix has the effect ofimproving wear resistance, the zinc equivalent of Si is 10, which isextremely high among those of elements added in high-strength brassalloy. Thus, since addition of Si increases the zinc equivalent, theamount of addition of another element is restricted in order to maintainthe matrix of single-phase structure of β phase. Here, as anotherelement, Al is known for example. Al improves corrosion resistance andstrengthens the matrix. However, the zinc equivalent of Al is extremelyas high as 6. Thus, when the amount of addition of Al increases, γ phaseappears in the matrix. Thus, when Al is added together with Si mentionedabove, the zinc equivalent increases and γ phase is produced in thematrix. As a result, although wear resistance increases, ductilityreduces extremely. Thus, even when it is tried to improve wearresistance by adding Si, it is unavoidable to reduce the amount ofaddition of Al. Thus, it was difficult to improve wear resistance whilemaintaining single-phase structure of β phase.

After great deal of effort has been made considering the abovecircumstances, the present inventors have focused on Cr as an elementthat improves corrosion resistance and at the same time generates theintermetallic compound of Fe and Si, which are ingredients of thehigh-strength brass alloy. The present inventors have confirmed that inhigh-strength brass alloy to which Cr is added in a prescribedproportion, the matrix maintains single-phase structure of β phase, andFe—Cr—Si-based intermetallic compounds have been dispersedlyprecipitated, and have found that corrosion resistance and wearresistance of the high-strength brass alloy have been improved further.

The present invention has been made on the basis of the above findings.And an object of the present invention is to provide the high-strengthbrass alloy for the sliding member, which maintains the matrix ofsingle-phase structure of β phase, has structure in which Fe—Cr—Si-basedintermetallic compounds are dispersed in the β phase, and thus issuperior in wear resistance. Another object of the present invention isto provide the sliding member using that high-strength brass alloy.

Solution to Problem

To achieve the above objects, the present invention provideshigh-strength brass alloy for sliding member, wherein:

(1) the high-strength brass alloy comprises, in terms of mass ratios, Znin a range of from 17% or more to 28% or less, Al in a range of from 3%or more to 10% or less, Fe in a range of from 1% or more to 3% or less,Cr in a range of from 0.1% or more to 4% or less, Si in a range of from0.5% or more to 2% or less, and the remnant including Cu and inevitableimpurities; and(2) a matrix shows single-phase structure of β phase, and structure inwhich Fe—Cr—Si-based intermetallic compounds are dispersed in the βphase.

Further, to achieve the above objects, the present invention provides asliding member, wherein:

(3) the sliding member has a cylindrical body made of the high-strengthbrass alloy for sliding member described in the above (1) and (2); aplurality of holes or grooves are formed at least in an inner peripheryas a sliding surface of the cylindrical body; and solid lubricant isfilled and fixed in the holes or grooves.

Further, to achieve the above objects, the present invention providesanother sliding member, wherein:

(4) the sliding member has a plate body made of the high-strength brassalloy for sliding member described in the above (1) and (2); a pluralityof holes, grooves or recesses are formed in a surface as a slidingsurface of the plate body; and solid lubricant is filled and fixed inthe holes, grooves or recesses.

Further, it is favorable that:

(5) an area of the solid lubricant is in a range of from 10% or more to40% or less of an area of the inner periphery or the surface as thesliding surface.

Advantageous Effects of Invention

According to the present invention, the matrix shows single-phasestructure of β phase, and, in that structure, hard Fe—Cr—Si-basedintermetallic compounds are dispersed in the β phase. Thus, it ispossible to provide the high-strength brass alloy having increasedhardness and further-improved wear resistance and to provide the slidingmember using the high-strength brass alloy.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view showing a plate-shaped sliding member of anembodiment of the present invention;

FIG. 2 is a cross section showing a cylinder-shaped sliding member of anembodiment of the present invention;

FIG. 3 is a cross section showing another example of cylinder-shapedsliding member of an embodiment of the present invention; and

FIG. 4 is a perspective view showing a method of testing wear amount inan embodiment of the present invention.

REFERENCE SIGNS LIST

-   1, 1 a, 1 b sliding member-   2, 2 a, 2 b sliding member substrate-   3, 3 a, 3 b sliding surface-   4 recess-   4 a groove-   4 b hole-   5 solid lubricant

DESCRIPTION OF EMBODIMENTS

Next, the present invention and its embodiments will be describedfurther in detail. Needless to say, the present invention is not limitedto these embodiments.

According to the present invention, a high-strength brass alloy for asliding member comprises, in terms of mass ratios, Zn: 17-28%, Al:3-10%, Fe: 1-4%, Cr: 0.1-4%, and Si: 0.5-3%, with the remnant includingCu and inevitable impurities. In the following, a component compositionof the high-strength brass alloy of the present invention will bedescribed.

Zn is an element that contributes to strength, wear resistance andcorrosion resistance to lubricating oil and determines structure of thematrix. According to the amount of addition of Zn, there appears a phasesuch as α phase, β phase or γ phase in the structure of the matrix. Theamount of addition of Zn varies depending on the zinc equivalents andthe amount of addition of the other added elements. When, however, theamount of addition of Zn is less than 17% by mass, α phase appears inthe structure of the matrix, deteriorating the wear resistance. On theother hand, when the amount of addition of Zn is larger than 28% bymass, γ phase appears in the structure of the matrix, making the alloybrittle. Thus, the amount of addition of Zn is 17-28% by mass.

Al is an element that promotes generation of β phase and effective forincreasing the hardness. Further, similarly to Si, the zinc equivalentof Al is large and Al assists generation of γ phase structure. However,when the amount of addition of Al is less than 3% by mass, sufficienthardness required for wear resistance cannot be obtained, and alsosufficient strengthening of the matrix cannot be attained. On the otherhand, when the amount of addition of Al is larger than 10% by mass, γphase structure is generated, making the alloy brittle. Thus, the amountof addition of Al is 3-10% by mass, and favorably 4-6% by mass.

Fe binds with the below-mentioned Si and Cr and precipitates hardintermetallic compounds of Fe—Cr—Si-based, to improve wear resistance.When the amount of addition of Fe is less than 1% by mass, the amount ofthe precipitation of Fe—Cr—Si-based intermetallic compounds is small,and thus its improvement effect on wear resistance is insufficient. Alsominiaturization of alloy structure is impaired and mechanical propertiescould be deteriorated. On the other hand, when the amount of addition ofFe is larger than 4% by mass, the amount of the precipitation ofFe—Cr—Si-based intermetallic compounds is large, to reduce wearresistance indeed. Thus, the amount of addition of Fe is 1-4% by mass.

Cr binds with the above-mentioned Fe and the below-mentioned Si toprecipitate hard Fe—Cr—Si-based intermetallic compounds, and thuscontributes to improvement of wear resistance. When the amount ofaddition of Cr is less than 0.1% by mass, Cr does not contribute toimprovement of wear resistance. On the other hand, when the amount ofaddition of Cr is larger than 4% by mass, it causes worsening ofmachinability and castability. Thus, the amount of addition of Cr is0.1-4% by mass.

Si binds with the above-mentioned Fe and Cr to precipitate hardFe—Cr—Si-based intermetallic compounds, and thus contributes toimprovement of wear resistance. When the amount of addition of Si isless than 0.5% by mass, Si does not contribute to improvement of wearresistance. On the other hand, when the amount of addition of Si islarger than 3% by mass, it causes appearance of γ phase, which mightworsen wear resistance. Thus, the amount of addition of Si is 0.5-3% bymass.

The high-strength brass alloy of the present invention can be castedinto a plate shape, to form a plate-like body. One surface of theplate-like body is used as a sliding surface, and a plurality of holesor grooves are formed in that surface. And solid lubricant such asgraphite is filled and fixed in the holes or grooves, to obtain asolid-lubricant-embedded type sliding member.

FIG. 1 is a plan view showing a sliding member (sliding plate) 1 havinga plate-like shape formed of the high-strength brass alloy of thepresent invention. In one surface (sliding surface) of a sliding membersubstrate 2 of the high-strength brass alloy, are formed a plurality ofrecesses 4 recessed in the thickness direction. These recesses 4 areformed such that the sum of areas of the openings is 10-40% of thesurface area of the sliding member substrate 2.

The recesses 4 are for the purpose of being filled with and holdingsolid lubricant 5 such as graphite. In order that the substrate 2 andthe solid lubricant 5 produce good wear resistance effects, the sum ofthe areas of the openings of the recesses 4 should be at least 10% ofthe total area of the surface of the sliding member substrate 2.However, when the sum of the areas of the openings of the recesses 4exceeds 40% of the surface area of the sliding member substrate 2, thestrength of the sliding member substrate 2 deteriorates. The recesses 4are formed by drilling work or cutting work using a drill or an endmill, although another means can be used to form the recesses 4.

Favorably the solid lubricant 5 filled and held in a plurality ofrecesses 4 formed in the surface of the sliding member substrate 2 isarranged such that a plurality of the solid lubricants 5 which adjoinmutually overlap with each other (with overlap length δ) in onedirection or two orthogonal directions.

FIG. 1 shows an example where the solid lubricant 5 filled and held in aplurality of recesses 4 formed in the surface of the sliding membersubstrate 2 is arranged such that a plurality of the solid lubricants 5which adjoin mutually overlap with each other in two orthogonaldirections.

Further, the high-strength brass alloy of the present invention can becast into a cylindrical shape, to form a cylindrical body. A pluralityof holes or grooves are formed at least in an inner periphery as asliding surface of the cylindrical body, and solid lubricant such asgraphite is filled and fixed in the holes or grooves, to obtain asolid-lubricant-embedded type sliding member.

FIG. 2 is a cross section showing a sliding member (cylindrical bearing)1 a having a form of a cylindrical bush that was made using thehigh-strength brass alloy of the present invention. In an innerperiphery (sliding surface) 3 a of a sliding member substrate 2 a of thehigh-strength brass alloy, are formed a plurality of grooves 4 a of ringshapes arranged in the longitudinal direction. Similarly to the case ofthe above-described sliding member 1, these grooves 4 a are formed suchthat the sum of areas of the openings of the grooves 4 a is 10-40% ofthe area of the inner periphery 3 a of the sliding member substrate 2 a.This ratio is selected for the same reason why the above-mentioned ratio10-40% is selected. The grooves 4 a are formed by cutting work using acutting tool or the like, although another means may be used to form thegrooves 4 a.

FIG. 3 is a cross section showing a sliding member 1 b having a form ofa cylindrical bush that was made using the high-strength brass alloy ofthe present invention. In the sliding member 1 b, are formed a pluralityof cylindrical holes 4 b passing through the sliding member 1 b from theinner periphery (sliding surface) 3 b to the outer periphery. And theseholes 4 b are filled with solid lubricant such as graphite. Similarly tothe case of the above-described sliding member 1, these holes 4 b areformed such that the sum of areas of the openings is 10-40% of the areaof the inner periphery 3 b of the sliding member substrate 2 b. Thisratio also is selected for the same reason why the above-mentioned ratio10-40% is selected. These holes 4 b are formed by drilling work using adrill or the like, although another means may be used to form the holes4 b.

It is favorable that the solid lubricant 5 is filled and fixed in theholes 4 b formed such that a plurality of the solid lubricants 5 whichadjoin mutually overlap with each other in the axial direction, or thatthe solid lubricant 5 is filled and fixed in the holes 4 b formed suchthat a plurality of the solid lubricants 5 which adjoin mutually overlapwith each other in the circumferential direction, or that the solidlubricant 5 is filled and fixed in the holes 4 b formed such that aplurality of the solid lubricants 5 which adjoin mutually overlap witheach other in the axial and circumferential directions.

FIG. 3 shows an example where the solid lubricant 5 filled and held in aplurality of holes 4 b formed in the sliding member substrate 2 b of acylindrical shape is arranged such that portions of the solid lubricant5 overlap with each other (with overlap length δ) in two directions i.e.the axial and circumferential directions.

Example 1

Next, the present invention will be described in detail referring toexamples. Of course, the present invention is not limited to thefollowing examples.

(1) Examples 1-5 and Comparative Examples 1-2

In order to obtain each chemical composition of Table 1, electrolyticCu, Zn, Al, Cu—Fe mother alloy, Si—Cu mother alloy, Cu—Cr mother alloyand Fe—Al mother alloy were melted in a low frequency melting furnace,and then casted into a sand mold of 50 mm in inner diameter, 80 mm inouter diameter and 100 mm in length at a melting temperature of 1100degrees Celsius or higher, to produce a cylindrical body. Then, thecylindrical body was subjected to machining process to produce acylindrical bearing of 60 mm in inner diameter, 75 mm in outer diameterand 50 mm in length. In the inner periphery of the obtained cylindricalbearing, a plurality of through holes of 10 mm in diameter were formedin the thickness direction such that the total opening area of the holeswas 30% of the area of the inner periphery. And, solid lubricantcomprising graphite was filled in these through holes. Next, thesolid-lubricant parts were vacuum-impregnated with lubricant oil, toobtain a specimen for wear test. As for hardness (Brinell hardness), thehigh-strength brass alloy part of the wear test specimen was measured.

(2) Comparative Examples 3-4

In order to obtain each chemical composition of Table 1, electrolyticCu, Zn, Al, Cu—Fe mother alloy, Ni—Al mother alloy, Si—Cu mother alloy,Mn—Cu mother alloy and Fe—Al mother alloy were melted in a low frequencymelting furnace, and then casted into a sand mold of 50 mm in innerdiameter, 80 mm in outer diameter and 100 mm in length at a meltingtemperature of 1100 degrees Celsius or higher, to produce a cylindricalbody. Then, the cylindrical body was subjected to machining process toproduce a cylindrical bearing of 60 mm in inner diameter, 75 mm in outerdiameter and 50 mm in length. Thereafter, similarly to the aboveexamples, a specimen for wear test was prepared. Further, as forhardness (Brinell hardness), the high-strength brass alloy part of thewear test specimen was measured.

Table 2 shows mechanical properties (degrees of Brinell hardness) andwear amount of the cylindrical bearings obtained in the above-describedExamples and Comparative Examples. In Table 2, wear amount of each weartest specimen was measured by journal oscillation test shownschematically in FIG. 4. The test method was as follows. That is to say,a rotating shaft (opposite member) B was rotated in oscillation againsteach of the cylindrical bearings A of the above-described Examples andComparative Examples. A load was applied and fixed to a cylinder bearingA while the rotating shaft B is rotated in oscillation at a constantsliding speed, to measure wear amount (μm) of the cylindrical bearing Aand the rotating shaft B after the predetermined test period. The testconditions were as follows.

(3) Test Conditions

Sliding speed: 0.47 m/min

Surface pressure: 1000 kgf/cm² (98 MPa)

Test time: 100 hours

Movement pattern: Oscillating movement

Oscillation angle: ±45°

Material of opposite member: SC steel (S45C)

Lubricating condition: lithium grease was applied to the sliding surfaceat the start of the test

TABLE 1 Table 1 Chemical composition (% by mass) Co Zn Fe Al Cr Si Mn NiMatrix Example 1 Residual 26.2 1.44 4.94 0.9 0.51 — — β phase 2 Residual25.8 1.63 4.78 3.57 1.38 — — β phase 3 Residual 24.11 1.52 4.02 3.211.88 — — β phase 4 Residual 22.31 1.23 4.88 1.96 0.93 — — β phase 5Residual 22.87 2.03 5.47 1.78 1.12 — — β phase Comparative 1 Residual 2705 0.83 2.95 0.75 0.44 — — α + β Example phase 2 Residual 26.08 3.027.43 1.8 1.32 — — β + γ phase 3 Residual 23.2 3.05 6.07 — 0.09 2.98 1.51β phase 4 Residual 15.03 3.09 5.98 — 1.47 6.06 2.03 α + β phase

TABLE 2 Wear amount (μm) Brinell hardness (HB) Bearing Opposite memberExample 1 212 25 1 2 215 24 0 3 213 27 0 4 220 22 0 5 223 21 1Comparative 1 185 95 1 Example 2 284 35 12 3 235 63 0 4 234 182 4

As for the high-strength brass alloys of the Examples of the presentinvention, each matrix shows single-phase structure of β phase and showsstructure in which hard Fe—Cr—Si-based intermetallic compounds aredispersed in the β phase. As a result, each example of the high-strengthbrass alloy is superior in wear resistance. It was confirmed that thesolid-lubricant-embedded type sliding members obtained by embeddingsolid lubricant in the high-strength brass alloys showed superior wearresistance when used as bearings, due to the superior wear resistance ofthe high-strength brass alloys as base metal in combination with the lowfrictional property of the solid lubricant.

On the other hand, as for the high-strength brass alloy of theComparative Example 1, its matrix shows α+β phase and thus its hardnessis low, and causes larger wear amount of the bearing itself. As for thehigh-strength brass alloy of the Comparative Example 2, its matrix showsβ+γ phase and its hardness is high, and causes smaller wear amount ofthe bearing itself. But on the other hand, damage to the opposite memberis large, and causes wear of the opposite member. Further, as for thehigh-strength brass alloy of the Comparative Example 3, its matrix showssingle-phase structure of β phase. However, intermetallic compoundsdispersed in the β phase are Fe—Cu—Al-based intermetallic compounds, andit is found that a sliding member in which solid lubricant is embeddedhas inferior wear resistance by increasing of its own wear amount.Further, the high-strength brass alloy of the Comparative Example 4 hasmarkedly-reduced wear resistance although Fe—Mn—Si-based intermetalliccompounds are dispersed in the matrix. This is considered to be due tosmall amount of Zn added to the high-strength brass alloy and appearanceof α phase in the β phase of the matrix.

INDUSTRIAL APPLICABILITY

As described above, the high-strength brass alloy of the presentinvention has the matrix showing single-phase structure of β phase, inwhich Fe—Cr—Si-based intermetallic compounds are dispersed in the βphase, and thus has improved wear resistance. So the high-strength brassalloy of the present invention can be applied to sliding purposes suchas a sliding bearing, a washer, a sliding plate and the like.

The invention claimed is:
 1. A high-strength brass alloy for slidingmember, wherein: the high-strength brass alloy consists only of, interms of mass ratios, Zn in a range of from 17% or more to 28% or less,Al in a range of from 3% or more to 10% or less, Fe in a range of from1% or more to 4% or less, Cr in a range of from 0.1% or more to 4% orless, Si in a range of from 0.5% or more to 3% or less, a remnantincluding Cu, and inevitable impurities; and a matrix shows single-phasestructure of β phase, while in the structure Fe—Cr—Si-basedintermetallic compounds are dispersed in the β phase.